Back solving to determine LCC parameters

drogers

Posted 10 February 2011 - 04:46 PM

drogers

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Hi,

I have a map projection that shows cloud cover data over eastern Canada (Link: http://www.weatherof...TRO_nt_003.png)What I would like to do is determine what pixel is equivillent to a given lat/long. I have e-mailed Environment Canada to ask for the parameters but recieved the following response:

"For the lat-long, these are forecast image and not actual satellite images. We utilize a polar stereographic projection for all the astro-forecast images. Iguess you will have to create the interface to convert lat and long for each pixel."

So I am left to determine the parameters myself. I believe that this map projection is zoomed in on a larger map projection similar to the one in this link: http://www.weatherof...STRO_uv_003.png

Does anyone have any good ideas of how I might be able to determine what pixil is equivilent to a particular lat/long?

Thanks for any information/help you can provide.

Regards,Dan Rogers

*Edit- The above link does not work anymore (My mistake) The map projections can be accessed from here: http://www.weatherof...clds_vis_e.htmlI am interested in the "Regional model, satellite simulation, Eastern Canada window"

drogers

Posted 11 February 2011 - 09:12 AM

drogers

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The first link doesn't leads to a map; the second one does. Without seeing the map ion question, it is difficult to answer your question.

Sorry about the bad link. They update these on a 24 hour basis and I didn't realize the address changes. Anyway, here is a link to the main page where I access the maps: http://www.weatherof...clds_vis_e.htmlI am particularly interested in the images from the "Regional model, satellite simulation, Eastern Canada window". If you click on any of the hours (i.e. "o3h") it will bring up the image.

Melita Kennedy

Posted 11 February 2011 - 08:06 PM

Melita Kennedy

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Your correspondent says it's polar stereographic. I get an image in ArcMap that looks pretty close by choosing a North pole-centered stereographic projection. Standard parallel is set to 75N, central meridian to 110W. You might ask them for the projection parameters and the sphere or ellipsoid they're using.

If you can't get any information on the sphere/ellipsoid or parameter values, you may be able to use the lat-lon corner values to georeference the raster. (Or project the lat-lon values into a polar stereographic and then georeference).

drogers

Posted 15 February 2011 - 08:30 AM

drogers

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Melita,

Thank you for your help. That Weather Office link was very useful. I wish I had been able to find it on my own. I think that the "Global GEM on full-resolution 30 km Polar Stereographic grid" matches the closest to my map of eastern Canada.

Now I am attempting to create a spreadsheet that will output X/Y coordinates for a given lat long. I found some formulas on wolfram (here: http://mathworld.wol...rojection.html). Any idea what the conformal latitude means? I don't see this parameter listed. Is it the centre latitude?

Edited @ 3:22 Tuesday FEB 15th 2011-I have created a spreadsheet with the required caclulations and get an output of X and Y-I noticed the X & Y coordinates are realted to the value I use for my radius. -How do I realte these XY coordinates with the map projection? The parameters state: